An electrical generator is a device that converts mechanical energy to electrical energy. The reverse conversion of electrical energy into mechanical energy may be performed by a motor, and motors and generators have many similarities. In the context of power generation, mechanical energy is typically provided to a generator by a combustion turbine or steam turbine.
A typical power generation plant may include a turbine, a generator, and an exciter. The turbine, generator, and exciter are connected together in axial alignment. The turbine converts fuel or heat energy into mechanical energy, in the form of turbine shaft rotation. The generator converts this rotational energy into electrical energy.
The generator includes a shaft and a rotor that rotates within a stator that surrounds the rotor. The rotor has a rotor body around which rotor windings are arranged. The stator has windings positioned parallel to the rotor windings. There is an electrically conductive stud extending radially outwardly from the shaft. An electrically conductive member couples the exciter to the rotor windings via the stud. As the rotor turns, an electrical current is induced in the stator windings. This induced electrical current is then drawn from the stator windings and is applied to an electric load or delivered to a distribution grid.
In the course of its service life, a generator will be subjected to numerous starts and stops. At each start or stop, substantial inertial and thermal stresses act upon the various components of the generator. The inertial stress and centrifugal force experienced by a component of the generator may depend upon the radial distance of the component from the axis of the rotor and the mass of the component. Therefore, different generator components may experience different magnitudes of these forces.
The electrically conductive path that carries current from the stud to the rotor windings is commonly known in the art as a J-strap. This J-strap is subjected to similar operating conditions and forces as the other generator components. Since different generator components experience different magnitudes of these forces, the J-strap may experience differential forces because different portions of the J-strap are connected to different generator components. J-strap failure due to this force differential at various points can be problematic, as such a failure can cause electric arcing and re-routing of the current through nearby electrically conductive materials, melting various components and otherwise damaging the generator.
One attempt at reducing J-strap failures focused on altering the generator rotor lead path. U.S. Pat. No. 6,501,201 to Whitener et al. discloses an apparatus that forms a conductive path for carrying an electric current in a generator. The apparatus includes an electrically conductive axial lead path that forms a portion of the conductive path. An electrically conductive strap forms another portion of the conductive path. Furthermore, a radial lead is coupled to the axial lead and the strap, forming yet another portion of the conductive path. The radial lead is not supported and restrained in the rotor.
Another attempt at reducing J-strap failure is disclosed in U.S. Pat. No. 7,129,605 to Zhang et al., which is directed to an interconnecting assembly for a rotor of an electric machine. This assembly is part of a conductive path extending from a radially inward section of the rotor assembly to a winding located at a radially outward section of the rotor assembly. The assembly includes a flexible member having a bend. A connector is coupled to the flexible member to pass axial and radial forces that develop during operation of the machine. The positioning of the connector relative to the flexible member may be arranged so that an effect of an axial force on a radius of curvature of the bend and an effect of a radial force on that radius of curvature are opposed to one another. This reduces mechanical stress on the flexible member.
However, other structures to enhance the longevity of a J-strap and to reduce the differential forces experienced thereby may be desirable.